Infrared studies of magnetic surface modes on antiferromagnets (invited)

In contrast to ferromagnets, where low frequency surface excitations typica lly have frequencies in the 10 GHz range, surface excitations in antiferrom agnets are often in the several hundred GHz to few THz range. Theoretical p redictions for surface spin waves on antiferromagnets indicate that they sh ould be highly nonreciprocal, i.e., the properties of a wave with wave vect or +k would be very different from those with a reversed wave vector of -k. Surface spin waves on antiferromagnets have recently been measured using a high resolution Fourier transform infrared spectrometer. The results show evidence of both true surface modes and surface resonances. The nonreciproc al features of the surface modes are seen in a dramatic nonreciprocal refle ction. For example, the reflectivity can be 80% for one orientation, but wh en the incident and reflected waves are reversed the reflectivity drops to near zero. While the initial measurements were done on a bulk antiferromagn et, we also present calculations showing the results for thin films. (C) 19 98 American Institute of Physics. [S0021-8979(98)36811-5].